Reimplement the kernel tracepoint facility. The new implementation is

Reimplement the kernel tracepoint facility.  The new implementation is
completely generic and very easy to implement in modules.  Compile-time
optimizations are retained and sysctl generation is completely automatic.
Only the DDB command code has been retained from FreeBSD.

The logging macros are designed to allow subsystems to trivially declare
and use the facility.

This implementation is not quite complete, we also want to integrate a
stack backtrace logging facility.